Fossil Plants With Microstructures From The Miocene Of Zhangzhou, Fujian And Palaeoclimatic Reconstructions

The global climate pattern has changed significantly since the Cenozoic,and the flora has also evolved.Because the Miocene was an important transitional period of the Cenozoic,it is important to discuss the relationship between global environment evolution,biological evolution,and climate change during the Miocene.Plant fossils provide not only the most direct evidence of biological evolution but also valuable materials for the study of paleoclimatic and paleoenvironmental changes.Wellpreserved plant fossils from the Cenozoic are found in the Miocene of Zhangzhou City,Fujian Province,one of the best preserved plant fossil areas at low latitudes in China.It is important to understand plant evolution and paleoclimatic characteristics at low latitudes in China during the Neogene.In the present study,macro-and microstructures of plant fossils(fruits,seeds,and leaves)in the Miocene from Zhangzhou,Fujian Province,were systematically studied,and the classification position of these fossils was confirmed by comparison with existing species using cluster analysis.The fossils were classified into 8 families,16 genera,and 37 species including 9 published new species(6 online new species)and 9 unpublished new species.Among these,we identified 5 families,13 genera,and 33 species as angiosperms;2 families,2 genera,and 2 species as ferns;and 2 species of epiphytic fungi.Combining the fossil records of the world,we discussed the origin and geographical changes of some important Fujian Fotan flora taxa.The paleoclimate characteristics of the representative tropical vegetation of Fotan were analyzed.Simultaneously,we quantitatively reconstructed and analyzed climatic factors in combination with leaf margin analysis(LMA)and climatic leaf analysis multivariate program(CLAMP).In this study,we report the world's first leaf fossil with three tips of Macaranga: M.zhangpuensis.The present fossil is the highest latitude record of Macaranga in the world.The leaf and fruit fossils of Lauraceae were also studied in detail,including 10 species from the following 4 genera: Alseodaphne,Laurophyllum,Cinnamomum,and Cryptocarya.These Lauraceae fruit fossils were the first to be reported and described from East Asia.The fruit morphology of these fossils was similar to that of the extant Cinnamomum fruit.A comparison between the fossil fruits and modern Cinnamomum fruit indicated little change in the morphology of Lauraceae since the middle Miocene.In addition,some well-preserved colonies of Meliolinites were found on the Lauraceae leaves,and 2 species M.fotanensii and M.zhangpuensis were identified.The Lauraceae leaf cuticle contained cells in the infected area that were thick and blur.Hence,it can be speculated that Meliolinites parasitize Lauraceae leaves and result in a stress response in the leaves.Two species of Garcinia,G.sp.(fruit)and G.zhangpuensis(leaf),were identified and described in this study.To the best of our knowledge,the microstructure of Garcinia leaf fossils was determined for the first time in the world.We also identified 3 species of Calophyllum,C.zhangpuensis,C.striatum,and C.suraikholaensis,indicating that Calophyllum began to diversify in Fujian Province during the Miocene.The research area had abundant fossils of leguminous pods,and 4 species of 3 genera were identified and described.Ormosia zhangpuensis sp.nov.is currently the earliest and lowest-latitude Ormosia fossil record in China.Cercis zhangpuensis sp.nov.is currently the lowest-latitude Cercis fossil record in Asia.In addition,we have obtained and described the microstructures of Ormosia,Cercis,and Acacia pod fossils for the first time.These microstructure descriptions bridge the knowledge gaps of previous microstructure studies.We also identified and described 13 species of 3 genera of fruit and leaf fossils of Fagaceae,including Castanopsis,Quercus,and Lithocarpus.Two new species of Castanopsis were established: C.fotanensis sp.nov.and C.paracarlesii sp.nov.These fossil species showed that Fagaceae found in Fujian Province diversified since the Miocene.In addition,a detailed study was conducted on the ferns in the Fotan flora,and 2 new species were identified: Osmunda zhangpuensis sp.nov.and Lygodium paramicrophyllum sp.nov.We provided the first in situ spores description of the microstructure of L.paramicrophyllum sp.nov.in China.This description enhanced our understanding of the microstructure of Lygodium fertile fronds found not only in China but also in Asia.The paleogeographic analysis of plant fossils in this study area is important for understanding the structural evolution of the surrounding areas of China,global climate change,and exchange between components of Indian flora and southeastern Chinese flora during the Miocene.Based on a large number of fossil records,we analyzed the origin and geographical changes of approximately 8 plant taxa,including Macaranga,Ormosia,Acacia,Cercis,Garcinia,Calophyllum,Lygodium,and Osmunda.These fossils reduced their distribution scope within the low-latitude region,which is consistent with the overall climate cooling from the Paleogene to the Neogene.A land connection was created by the collision of the Indian and Eurasian plates that enabled interactions between Indian flora and southeastern Chinese flora during the Miocene.Finally,based on the 86 morphotypes of the woody dicotyledonous plants from the Fotan flora,the paleoclimate during the Miocene in Zhangpu,Fujian Province,was quantitatively reconstructed using LMA and CLAMP.The results showed that during the middle Miocene,the mean annual temperature of the Fotan area was approximately 1.5°C–3°C higher than the current temperature.The precipitation during the growing season was approximately 161.2–1063.6 mm higher than the current precipitation values.This indicated that during the middle Miocene,the Fotan area was warmer and wetter than it is today.Quantitative reconstruction of monsoon indicators showed that seasonal changes in the Fujian Province in the middle Miocene are comparable to those observed currently.The study area also reported a new species in Macaranga with three tips(the highest latitude record in the world),Alseodaphne,Garcinia,and Calophyllum with broadleaf,and other components of the tropical forest as well as defoliation plants of Cercis,Liquidambar,and Salicaceae.Based on the results of quantitative paleoclimate reconstruction and fossil plant association,it was hypothesized that Zhangzhou,Fujian Province,had a tropical monsoon forest climate during the middle Miocene.